Saturday, 1 March 2014

What is an entity?- AnEntity is the distinct object in the organization and that is to be represented in database.There are 2 types of entities.Strong and weak entity.Entity type that do not have any key attributes are known as weak entity type but regular entity type that have key attributes are known as strong entity.

What is an attribute?- Anattribute is that which describe some aspect of the object that we wish to record.

Types of attributes:-

1. Single value attributes:- These are the attribute that have single value.

2. Composite attributes:- It composed of multiple components.e.g

3. Simple attributes:- It is an attribute that composed of a single component with an independent existence. These attributes can't be further sub-divided.e.g age,rollno.

4. Multi-valued attributes: It can hold multiple value for a single attribute. e.g phone no

TYPES OF OBJECT BASED DATA MODELS:-There are 4 types of Object based data models:-

1.) ER(entity relationship) model

2.) Object oriented ER model

3.) Semantic model

4.) Functional model

1.) ER MODEL(entity relationship model)(Top-down approach):-It is the graphical technique i.e. used to convert the requirements of the system to a graphical representation for easy understanding.It is a conceptual model that used the objects as entity, attributes and relationships.Its basic component is ER diagram.It is simple and easy to understand .It can be easily converted to other models.

ER NOTATIONS:-

HOW TO DESIGN AN ER DIAGRAM:- EG. BANKING SYSTEM

2.) OBJECT ORIENTED ER MODEL:-The object oriented data model extends the definition of an entity to include,not only the attributes that describe the state of the object but also the actions that are associated with the object,that is its behavior.The object is said to encapsulate both state and behavior.

3.) SEMANTIC MODEL:- It is used to express greater inter-dependencies among the entities of interest.These inter-dependencies enable the model to represent semantics of the data in DB.This class of data models is influenced by the work of artificial intelligence researches semantic data model. It is developed to organize and represent knowledge not data. In coming times,DBMS will be fully partially intelligent

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